The present invention relates, in general, to glass bonding to ceramic materials, and more particularly, to glass bonding to non-oxide ceramic materials used in electronic packages.
Electronic packages provide mechanical support, electrical connection, and a means for dissipating heat for integrated circuits. Mechanical support is necessary to facilitate handling and prevent breakage of the integrated circuit during installation or operation of the device. Electrical connections on the packages provide power inputs, interconnects between devices, ground planes, and the like. Heat dissipation is required to avoid severe thermal excursions which would result in decreased reliability and device failure.
Semiconductor trends include increased function density, power density, and speed. These trends create a need for electronic packages having increased wiring density and improved thermal management capability. Many high frequency electronic packages require components comprising low dielectric constant materials. Low dielectric constant materials decrease signal propagation delays in the conductor lines. Lower dielectric constants also decrease electrical noise resulting from capacitance between adjacent conductor lines.
Thermal performance of the package is also an important consideration. High thermal conductivity is desired to avoid severe heating of the device, which can compromise both performance and reliability. Coupled with this is a desire to match thermal expansion of various package components, since some heating is unavoidable. Poor thermal expansion matching can result in substantial stress and mechanical failure at the interfaces between package components.
Ceramics are often chosen for high reliability package components because, in general, they provide the best compromise between dielectric constant and thermal conductivity while being relatively cost competitive for high performance devices. Ceramic packages offer the capability of producing a hermetic package, which can provide superior protection of the IC from harsh environmental conditions and is often required for high reliability applications. Ceramics also have a higher flexure strength than plastic packages and so provide more mechanical protection for the semiconductor chips.
Alumina (Al.sub.2 O.sub.3) and beryllia (BeO) are the most commonly used ceramics for electronic packages. Although Al.sub.2 O.sub.3 has relatively low thermal conductivity, it is most often chosen because it is very low cost. BeO provides significantly higher thermal conductivity and significantly lower dielectric constant, however, BeO dust is extremely toxic. Toxicity of BeO has limited its development. Further, both alumina and beryllia have relatively low flexure strength compared to other known ceramics and do not closely match the thermal coefficient of expansion of silicon, a common material used for semiconductor devices.
Accordingly, it is desirable to have a ceramic having high thermal conductivity, high flexure strength, and coefficient of thermal expansion closely matching that of silicon. It is also desirable to have a ceramic material which is compatible with electronic packaging processes for attaching semiconductor chips, leadframes and heatsinks to the ceramic.